1. Technical Field
The disclosure relates to an endoscope system including an imaging element for outputting, as pixel information, an electrical signal after photoelectric conversion from a pixel arbitrarily specified as a reading target, among a plurality of pixels for imaging.
2. Related Art
Conventionally, in the medical field, endoscope systems have been used when an observation of an organ of a subject such as a patient is performed. The endoscope systems include an insertion unit that is inserted into a body cavity of the subject, an imaging unit that is provided at a distal end of the insertion unit and captures an in-vivo image, and a display unit that can display the in-vivo image captured by the imaging unit. To acquire the in-vivo image, using the endoscope systems, the insertion unit is inserted into the body cavity of the subject, and then predetermined illumination light is irradiated from the distal end of the insertion unit, and the imaging unit captures the image.
In recent years, complementary metal oxide semiconductor (CMOS) image sensors have been applied as the imaging unit (see Japanese Laid-open Patent Publication No. 2010-68992, for example). In the CMOS image sensors, the way of reading out the pixel information based on electric charges accumulated in the pixels can be arbitrarily set. Therefore, the CMOS image sensor can perform a wider variety of imaging than a charge coupled device (CCD) image sensor that reads out all of the pixels at the same time.
FIG. 12 is a diagram schematically illustrating an outline of an image acquisition method performed by a conventional endoscope system using a CMOS image sensor. In FIG. 12, periods P1, P2, and P3 respectively represent an exposure period of each horizontal line, a transfer period of an image signal after exposure, and a reset period in which a reset signal occurs. Further, in FIG. 12, a frame cycle Tf and a reset cycle Tr are equal.
If the CMOS image sensor is employed, an image signal and a reset pulse group are transferred or occur in each horizontal line. Therefore, a time difference in signal occurrence is caused between a first horizontal line and a last horizontal line (ΔT of FIG. 12).